Alternate fuels have been developed to mitigate the rising prices of conventional fuels and for reducing exhaust emissions. For example, natural gas has been recognized as an attractive alternative fuel. For automotive applications, natural gas may be compressed and stored as a gas in cylinders at high pressure. A pressure regulating valve may then be used to supply the compressed natural gas (CNG) at lower pressures to an engine combustion chamber.
Various fuel sensors may be included in both conventional and alternate fuel engine systems, in order to monitor fuel storage amounts and regulate the metering of the fuel to the engine. To ensure each fuel sensor is functioning properly, rationality checks may be carried out under certain conditions, where the output of each fuel sensor is compared to the output of certain other engine sensors. If the fuel sensor output does not match the output of the other engine sensors, degradation of the fuel sensor may be indicated.
However, the inventors herein have recognized a potential issue with such an approach. Due to the expansion of CNG fuel through a regulator before reaching a fuel rail, cooling of the CNG fuel may occur. This cooling may hinder correlation between the temperature measured by a fuel rail temperature sensor and temperature measured by other engine sensors, such as engine coolant temperature. Thus, degradation of the fuel rail temperature sensor may be difficult to detect.
In one example, some of the above issues may be at least partly addressed by an engine method. In one embodiment, the method includes delivering gaseous fuel to a cylinder based on feedback from a fuel rail temperature sensor, and during select conditions, indicating fuel rail temperature sensor degradation based on a difference between measured fuel rail temperature and an expected temperature.
In this way, a rationality check may be performed on the fuel rail temperature sensor, configured to measure the temperature of a gaseous fuel such as compressed natural gas, while the engine is operating. In one example, the temperature measured by the fuel rail temperature sensor may be compared to the measured underhood temperature during idle engine operation. If the two temperature measurements differ by more than a threshold amount, fuel rail temperature sensor degradation may be indicated, and various mitigating actions taken in response the indicated degradation.
Furthermore, in a bi-fuel vehicle, a similar approach may be taken when the gaseous fuel system is not in use (but the other fuel system, e.g., gasoline system, is in use). When not in use, the gaseous fuel componentry tends to be equal to the underhood temperature, and thus the gaseous fuel rail temperature may be compared to the underhood temperature in order to determine if the rail temperature sensor is degraded. This temperature rationality action may supplement the inter-temperature sensor correlation checks that occur at the “key-on after a long temperature soak” condition, e.g., during idle operation. Another condition that can be used for fuel rail temperature rationality check is whether the fuel rail temperature is below underhood temperature at a condition of an extended medium to high fuel rate, where the cold fuel has a chance to cool the conduits in which it is conducted.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.